The proposed study aims 1) to characterize the distribution of initial binding sites for selected gonadotrophic hormones on target cells, 2) to characterize subcellular relationships between saturable binding sites and adenylate cyclase activity, 3) to evaluate the intracellular fate of these hormones, and 4) to explore microvascular and intercellular relationships during the inductive phase of hormone effects on the ovary. To this end electron microscopy (EM), EM radioautography of radioiodinated hormones, and EM cytochemistry of adenylate cyclase activity will be used. The aspects relating to the objective No. 4 will be studied by in vivo injection of horse radish peroxidase, and by lanthanum nitrate impregnation of fixed tissues.